Elemental Proliferation

In other words, is it possible to sustain Shock charges on a high-HP monster independently from the low-HP monsters who initially caused the high-HP monster to be 'Shocked'?

And to return to your final question:
I guess it should be very well possible given the lightning damage you inflict on the high-HP monster is increased to a sufficiently high level by the shock stacks from the Low-HP monsters.

It seems like the fire EP "aura" stacks. That is if you have 6 burning enemies each creating a burning "aura", each enemy takes damage as if it had a burn equal to the sum of all those burns, NOT the most powerful burn.

It seems like the fire EP "aura" stacks. That is if you have 6 burning enemies each creating a burning "aura", each enemy takes damage as if it had a burn equal to the sum of all those burns, NOT the most powerful burn.

Is this intended?

From what I can tell using fire trap with EP, there is a damage increasing effect but it's not a simple stacking. I suspect that what happens is that when multiple targets are ignited with overlapping EP effects the strongest one takes effect (as should happen with ignite). Since fire trap has quite a large damage range, when you hit lots of targets you get a higher chance of hitting the top of that range since there's more rolls and all targets will take the highest proliferated ignite. So you will see higher ignite damage when you EP multiple targets, but not close to stacking.

If you really want to take advantage of this same effect you can mix multiple packs of mobs together - they will all burn for the equivelant damage of whichever mob has the lowest fire resistance, since ignite doesn't directly check against a target's fire res. if you ignite 2 targets, 1 with 50 fire res and 1 with -50 fire res, they will both burn for the value of the the target with -50 res.

It seems like the fire EP "aura" stacks. That is if you have 6 burning enemies each creating a burning "aura", each enemy takes damage as if it had a burn equal to the sum of all those burns, NOT the most powerful burn.

Is this intended?

From what I can tell using fire trap with EP, there is a damage increasing effect but it's not a simple stacking. I suspect that what happens is that when multiple targets are ignited with overlapping EP effects the strongest one takes effect (as should happen with ignite).

This is correct. Whenever something is affected by multiple instances of the 'burning' status ailment, the highest damage one takes effect and the others are 'inactive' until that runs out, at which point the highest remaining one takes over.

Line of Sight does not appear to be functioning properly on this ability. The effect almost seems to originate from the ground or target the opponent's feet because tiny hills can prevent the spread entirely of the elemental proliferation.

The term Hit refers to skills which hit opponents and trigger on-hit effects. Apart from damage, on-hit effects include inflicting status ailments, gaining charges, stunning or knocking back enemies, gaining life or mana, and skill-specific effects like Infernal Blow's explosion.

I find the wording "apart from damage" to be pretty strange. It seems to imply that a hit can be registered simply by spreading status ailments via elemental proliferation, even if no damage is done. Additionally, it seems to imply that something like power siphon will register a hit as well if someone else kills the mob shortly after you hit it and get a power charge, even if they deliver the kill after you hit the mob. (Notice that these "effects" do not require a target to be separately damaged for the effects to occur.) For example, lightning arrow with LMP hits 12 mobs, and with elemental proliferation, each mob has 3 shock stacks. It would seem to imply that under this scenario, that each mob was "hit" 3x.